Plastics are used in a wide variety of molding applications for the preparation of molded articles for use in the automotive, industrial and appliance markets, among others. Vehicles, for example, include many interior and exterior parts and attachments that are constructed from plastics, such as mirror casings, fenders, bumper covers, spoilers, dashboards, interior trim, etc. The preparation of such articles generally includes the steps of molding an article from a polyolefin or other resin and applying to the molded article one or more film-forming coating layers to protect and/or color the article.
One of the difficulties associated with the use of plastic substrates is that typical film-forming compositions used for protective and decorative coatings do not adhere well to such substrates. A solution to this problem is to include a layer of a composition that includes an adhesion promoting material, such as a chlorinated polyolefin (“CPO”), between the substrate and the film-forming coating.
In refinishing molded articles constructed from plastics, for example, the need to include a layer of a composition that includes an adhesion promoting material can make the refinishing process complex, time-consuming, and expensive. Historically, the refinishing of such articles, such as automobile parts, has involved several steps. First, the surface to be refinished is cleaned, such as with a detergent, and allowed to dry. Second, the surface is wiped with a solvent, such as an alcohol. Third, the surface is scuffed, often using sandpaper or an abrasive pad to promote mechanical adhesion of subsequent materials. The scuffing step sometimes includes the addition of a sanding paste. Fourth, the surface is rinsed with water and allowed to dry. Fifth, the surface is wiped with a solvent to, for example, remove dust, oil, fingerprints, etc. Sixth, the surface is wiped or sprayed with a composition containing an antistatic agent, which is then flashed to remove solvents from the composition. Next, a material containing a CPO is sprayed onto the surface and then flashed to remove solvents from the material. Finally, a protective and decorative coating system is applied to the surface and cured.
As is apparent, such refinishing processes are complex, can generate a significant amount of waste, and can be very labor intensive and time-consuming. Moreover, because a CPO is applied in only one step, usually by spray application, such processes can sometimes result in inconsistent adhesion results, particularly in an automobile body shop setting, because there is a significant possibility that a portion of the surface to be refinished is not covered by a sufficient amount of adhesion promoting material.
As a result, there is a need for improved methods and systems for coating articles having a plastic substrate.